The equilibrium constant for the reaction between ethanoic acid CH3COOH and water H2O can be determined using the dissociation constant Ka for ethanoic acid. The reaction can be written as:CH3COOH + H2O CH3COO- + H3O+The dissociation constant Ka is given as 1.8 x 10^-5 at 25C. In this case, the Ka value is the equilibrium constant for the reaction, as it represents the ratio of the concentrations of the products to the reactants at equilibrium. Therefore, the equilibrium constant K for the reaction between ethanoic acid and water is:K = Ka = 1.8 x 10^-5